The present invention relates generally to radiometric imaging technology, and more particularly, to high resolution imaging using passive systems and methods.
Microwave imaging is used to generate high resolution ground and ocean maps. Imaging with sufficiently fine resolution enables topographic features and objects of interest on the ground or sea to be recognized. Current high resolution imaging techniques include synthetic aperture radar (SAR), useful for far-field operation, and triangulation methods using several antennas that locate active emitters. However, passive systems are more advantageous, since they prevent detection when gathering data used for generation of these maps.
Synthetic aperture radar is designed to provide far-field imaging. Since cloud cover does not impair the effectiveness of synthetic aperture radar, this system provides high resolution ground mapping under various meteorological conditions. The resolution possible with SAR systems improves as the integration time and bandwidth are increased. However, synthetic aperture radar is an active system, and its presence may be detected.
One accepted method of passive imaging uses well known triangulation principles. Triangulation is a process of directional location of active emitters from several disperate positions. The resolution possible with this technique improves as the size of its antennas is increased. However, in order to have high resolution, very large antennas must be employed. Since triangulation involves at least three receiving locations, these systems are typically costly.
Therefore, a need exists for passive high resolution imaging systems that may be implemented using small antennas. There also exists a need for a passive system that is not readily detectable. It would also be desirable to have a passive system that provides imaging resolution comparable to that of synthetic aperture radar. Accordingly, it is an objective of the present invention to provide an interferometer imager that combines a large number of measurements to achieve extremely high resolutions rivalling those of synthetic aperture radar. A further objective of the invention is to provide a passive imaging system incorporating relatively small antennas. Still another objective of the present invention is to provide an imaging system that utilizes tomographic techniques. A still further objective of the invention is to provide a passive imaging system having a small number of antennas.